1. Industrial Field
The present invention relates to a pen exchanging mechanism of an automatic drafting machine.
2. Prior Art
According to the conventional mechanism for exchanging pens in an automatic drafting machine shown in FIG. 4, respective writing instrument holding means 2 of a stocker 1 consist of a stationary arm 3 and a rotary arm 4, and the writing instrument holding means 6 of the drawing head 5 consists of a pair of upper and lower stationary arms 7 and 8, and a rotary arm 9 situated at a mid position of the upper and the lower stationary arms. The rotary arms 4 and 9 are supported so as to turn around axes perpendicular to a face on which drawing operations are done, and urged to press a writing instrument 10 held by the stationary arms 3, 7 and 8 by means of springs (not shown).
A pen exchanging operation or the exchange of the writing instrument 10 between the writing instrument holding means 2 of the stocker 1 and the writing instrument holding means 6 of the drawing head 5 is automatically carried out through reciprocal motions of the drawing head 5 toward and leaving from the writing instrument holding means 6 along the direction of an arrow shown in FIG. 4. The principle of the conventional automatic pen exchanger has been known, for example, in detail from Japan Patent Application Laid-open No. 2-63080.
It is noted that the writing instrument holding function carried out at the writing instrument holding portion of the known drawing head is carried out through a three-point support technique of stationary arms and a rotary arm 39 (see FIG. 5). Accordingly, the writing instrument held at the drawing head 5 by the stationary arms and the rotary arm is unstable and not secured. It is necessary to increase the force of the spring installed for the rotary arm 39 in order to hold the writing instrument stably. However, when a strong spring is used for the rotary arm of the conventional automatic drafting machine of the flat bed type shown in FIG. 5, the rotary arm 39 of the drawing head 34 presses strongly against the writing instrument 38 and rubs it heavily when the drawing head 34 takes the writing instrument 38 held by the stationary arm 36 and the rotary arm 37, respectively, of the stocker 35, resulting in out of injuring the writing instrument 38. In addition, there is a fear of deforming the stationary arm 36 of the stocker 35 due to the strong pressure of the rotary arm 39 of the drawing head 34.
According to the conventional automatic drafting machine of the moving paper type in which writing instruments 43 are exchanged between a rotary type stocker 39 and a drawing head 40 as shown in FIG. 6 (A) and (B), before the rotary arm 42 of the drawing head 40 having a strong spring grips the writing instrument 43 placed on the stocker 39 in order to exchange writing instruments, the writing instrument 43 is strongly pressed by the movement force of the drawing head 40 as shown in particular in FIG. 6 6(B) resulting disadvantageously in an unintentional rotation or displacement of the stocker 39 from its stop position.